The present invention relates to a method of preparing a solution of gallium 68 in ionic form, which can be used directly in the medical field for preparing labelled pharmaceutical compositions intended for making certain clinical diagnoses, in particular, by techniques of tomography by positron emission.
It is known that positron emitters occupy a special place amongst the radioelements which can be used in nuclear medicine, since they lead to the coincident emission of two gamma photons, with which it is possible to obtain good quality tomographic images.
Radioelements of this kind generally have very short half-lives, which is an advantage from the point of view of dosimetry but presents certain problems in the clinical use of these radioelements in hospital centres which do not have the considerable facilities needed for their production.
Of these radioelements, gallium 68 is of great interest as it is a positron emitter with a half-life of 68.3 min., which is produced during the decay by electronic capture of germanium 68, which has a half-life of 280 days.
Thus, if it is possible to separate the daughter element gallium 68 from the parent element germanium 68, it is possible to produce an autonomous source of positron emitter with a short half-life, which decays only very slowly in the course of time owing to the long half-life of germanium 68, and which can be used several times a day, since the equilibrium between germanium 68 and gallium 68 is achieved in a few hours.
Up to now, the methods used for obtaining gallium 68 from germanium 68 have made use of extraction techniques using a solvent or chromatographic techniques.
In solvent extraction methods, gallium 68 is extracted in an organic solvent, for example in the form of a complex of acetyl acetone when the organic solvent is cyclohexane, or in the form of a 68 Ga-oxine complex when the organic solvent is chloroform.
In the separation processes using a chromatographic technique, germanium 68 can be fixed on a column of alumina and then the column can be eluted with a solution of ethylenediamine tetraacetic acid 0.005 M (EDTA) to recover the gallium 68.
These known processes have certain disadvantages. In fact, the processes which use a solvent extraction step lead to gallium solutions wherein the gallium is obtained in a sequestered form which cannot be used directly for labelling pharmaceutical preparations and therefore has to undergo additional treatments, generally resulting in a reduction in the available radioactivity. Moreover, during extraction by solvent, it is difficult to automate the separation of the aqueous and organic phases, with the result that there are considerable risks of irradiation and contamination.
The methods using chromatographic techniques do not produce very high yields of gallium 68; moreover, this yield decreases substantially as a function of time and again the gallium is obtained in sequestered form.